The anchor comprising a confinement member reaching to the bottom of a borehole predrilled in the soil in which the anchor is introduced and bonded with the surrounding soil by means of a hardening agent injected in said borehole, and fixed by the hardened agent in the soil, and a stressed tension member accommodated in an encasing tube reaching up to an anchoring plate covering said borehole from outside, a tube being placed in the center of said steel tendon along the entire length of the anchor, said tube being introduced simultaneously with said anchor into the borehole and means to perform the method.
The method of underpinning building grounds, support walls, embankments or similar by using prestressed rock or soil anchors is a widely used system used when constructing buildings below and above ground levels, by constructing roads and railways etc. Considerable supporting forces are needed in sliding areas to secure the soil masses threatening to drop, this can be achieved by means of prestressed rock or soil anchors by means of which the loads can be directly, absorbed.
To apply the soil anchors, holes will be driven first in the soil in which the anchors consisting of steel strands, wires or steel bars will be inserted. The fixing of an anchor in the ground site is carried out in such a way that the ends of the longitudinal elements of the anchor, which reach to the bottom of the borehole, will be connected with the surrounding soil be means of an injected cement grout. The remaining tension portion of the anchor is protected by a plastic sheath and is accordingly stressed as desired after the cement grout has been hardened.
In some cases, as when preparing a ground site, the anchors will be extracted from the soil after the building has been completed. In such cases it was usual to cut the anchor between its confinement and tension members. In this way it is possible to pull out the tension member of the anchor out of the soil. However, the confinement member with the injection body cannot be readily and pulled out of the ground along with the tension member out of the soil which is generally unsatisfactory. The grouted portion of the anchor which remained in the soil had to be excavated afterwards by means of a shovel dredger, a traxcavator or a loader. However, such an excavating work is very complicated because the cement mortar block surrounding the longitudinal elements consisting of strands, wires or bars can have a length of about five meters and a width of about one meter.
Another known prior art of extracting soil anchors out of the soil consists in using a boring machine with a round hollow drill having its inside diameter considerably larger than the outside diameter of the anchor. It will be drilled with the boring machine into the depth upto and including the hard cement mortar block whereafter the anchor can be pulled out of the soil as a whole. Even this method is disadvantageous because of the high costs, excessive noise, and comparatively large spaced required.